Support Apparatus for Microphone Diaphragm

ABSTRACT

A microphone includes a diaphragm assembly supported by a substrate. The diaphragm assembly includes at least one carrier, a diaphragm, and at least one spring coupling the diaphragm to the at least one carrier such that the diaphragm is spaced from the at least one carrier. An insulator (or separate insulators) between the substrate and the at least one carrier electrically isolates the diaphragm and the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/625,553 entitled SUPPORT APPARATUS FOR MICROPHONE DIAPHRAGM filed onJan. 22, 2007 in the name of Jason W. Weigold (Attorney Docket No.2550/B42), which is a continuation-in-part of U.S. patent applicationSer. No. 11/113,925 entitled MICROMACHINED MICROPHONE AND MULTISENSORAND METHOD FOR PRODUCING SAME filed on Apr. 25, 2005 in the names ofJohn R. Martin, Timothy J. Brosnihan, Craig Core, Thomas Kieran Nunan,Jason Weigold, Xin Zhang, now issued as U.S. Pat. No. 7,825,484(Attorney Docket No. 2550/A47), and also claims the benefit of priorityfrom U.S. Provisional Patent Application No. 60/760,854 entitled SUPPORTAPPARATUS FOR MICROPHONE DIAPHRAGM filed on Jan. 20, 2006 in the namesof Timothy J. Brosnihan, Xin Zhang, Craig Core, and Jason W. Weigold(Attorney Docket No. 2550/A97). The subject matter of U.S. patentapplication Ser. No. 11/366,941 entitled PACKAGED MICROPHONE WITHELECTRICALLY COUPLED LID filed on Mar. 2, 2006 in the names of KieranHarney, John R. Martin, and Lawrence Felton (Attorney Docket No.2550/A88), which claims priority from U.S. Provisional PatentApplication No. 60/708,449 entitled MICROPHONE WITH PREMOLDED TYPEPACKAGE filed on Aug. 16, 2005 in the names of Lawrence Felton, KieranHarney, and John Martin (Attorney Docket No. 2550/A74), may also berelevant to this application. The above-referenced patent applicationsare hereby incorporated herein by reference in their entireties.

This patent application may also be related to one or more of thefollowing listed United States patent applications, which are owned byAnalog Devices, Inc. of Norwood, Mass., all of which are herebyincorporated herein by reference in their entireties:

-   -   METHOD OF FORMING A MEMS DEVICE, naming Thomas Kieran Nunan and        Timothy J. Brosnihan, assigned attorney docket number 2550/A40,        filed Jan. 3, 2005, and having Ser. No. 11/028,249.    -   MICROPHONE WITH IRREGULAR DIAPHRAGM, naming Jason Weigold as        inventor, assigned attorney docket number 2550/A76, filed Aug.        23, 2005, and having Ser. No. 60/710,517,    -   MULTI-MICROPHONE SYSTEM, naming Jason Weigold and Kieran Harney        as inventors, assigned attorney docket number 2550/A77, filed        Aug. 23, 2005, and having Ser. No. 60/710,624,    -   MICROPHONE SYSTEM, naming Kieran Harney as inventor, assigned        attorney docket number 2550/A78, filed Aug. 23, 2005, and having        Ser. No. 60/710,515,    -   PARTIALLY ETCHED LEADFRAME PACKAGES HAVING DIFFERENT TOP AND        BOTTOM TOPOLOGIES, naming Kieran Harney, John R. Martin,        Lawrence Felton, assigned attorney docket number 2550/A87, filed        Jan. 24, 2006, and having Ser. No. 11/338,439.    -   MICROPHONE WITH ENLARGED BACK-VOLUME, naming Kieran Harney as        inventor, assigned attorney docket number 2550/A89, filed Nov.        28, 2005, and having Ser. No. 60/740,169.    -   MICROPHONE WITH PRESSURE RELIEF, naming Xin Zhang, Michael W.        Judy, Kieran P. Harney, Jason W. Weigold, assigned attorney        docket number 2550/B40, filed Jan. 17, 2007, and having Ser. No.        60/885,314.

FIELD OF THE INVENTION

The invention generally relates to microphones and, more particularly,the invention relates to support for microphone diaphragms.

BACKGROUND OF THE INVENTION

Microelectromechanical systems (“MEMS,” hereinafter “MEMS devices”) areused in a wide variety of applications. For example, MEMS devicescurrently are implemented as microphones to convert audible signals toelectrical signals, as gyroscopes to detect pitch angles of airplanes,and as accelerometers to selectively deploy air bags in automobiles. Insimplified terms, such MEMS devices typically have a movable structuresuspended from a substrate, and associated circuitry that both sensesmovement of the suspended structure and delivers the sensed movementdata to one or more external devices (e.g., an external computer). Theexternal device processes the sensed data to calculate the propertybeing measured (e.g., pitch angle or acceleration).

MEMS microphones are being increasingly used in a greater number ofapplications. For example, MEMS microphones are often used in cellularphones and other such devices. To penetrate more markets, however, it isimportant to obtain satisfactory sensitivity and signal to noise ratiosthat match more traditional microphones.

MEMS microphones typically include a thin diaphragm electrode and afixed sensing electrode that is positioned alongside the diaphragmelectrode. The diaphragm electrode and the fixed sensing electrode actlike plates of a variable capacitor. During operation of the microphone,charges are placed on the diaphragm electrode and the fixed sensingelectrode. As the diaphragm electrode vibrates in response to soundwaves, the change in distance between the diaphragm electrode and thefixed sensing electrode results in capacitance changes that correspondto the sound waves. These changes in capacitance therefore produce anelectronic signal that is representative of the sound waves. Eventually,this electronic signal may be processed to reproduce the sound waves,for example, on a speaker.

FIG. 1 shows the general structure of a micromachined microphone asknown in the art. Among other things, the micromachined microphoneincludes a diaphragm 102 and a bridge electrode (i.e. backplate) 104.The diaphragm 102 and the backplate 104 act as electrodes for acapacitive circuit. As shown, the backplate 104 may be perforated toallow sound waves to reach the diaphragm 102. Alternatively oradditionally, sound waves can be made to reach the diaphragm throughother channels. In any case, sound waves cause the diaphragm to vibrate,and the vibrations can be sensed as changes in capacitance between thediaphragm 102 and the bridge 104. The micromachined microphone typicallyincludes a substantial cavity 106 behind the diaphragm 102 in order toallow the diaphragm 102 to move freely.

Many MEMS microphones use a diaphragm that is anchored completely aroundits periphery, similar to the head of a drum. Such diaphragms canpresent a number of problems. For example, in the presence of soundwaves, such diaphragms tend to bow rather than move up and downuniformly, as shown in FIG. 2A. Such bowing can negatively affect thesensitivity of the microphone, specifically due to the limiteddisplacement of the diaphragm causes by internal tension and thevariation in distance between portions of the diaphragm and the fixedsensing electrode. Also, such diaphragms can suffer from sensitivity tostresses (e.g., heat expansion), which can distort the shape of thediaphragm and can affect the mechanical integrity of the diaphragm aswell as the sound quality produced by the microphone.

Some MEMS microphones have a diaphragm that is movably connected withits underlying stationary member (referred to hereinafter as a“carrier”) by way of a plurality of springs. The springs tend to enablethe diaphragm to move up and down uniformly (i.e., like a plunger), asshown in FIG. 2B.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention there is provided amicrophone having a substrate; a diaphragm assembly supported by thesubstrate, the diaphragm assembly including at least one carrier, adiaphragm, and at least one spring coupling the diaphragm to the atleast one carrier, the diaphragm being spaced from the at least onecarrier; and at least one insulator between the substrate and the atleast one carrier so as to electrically isolate the diaphragm and thesubstrate.

In various alternative embodiments, the substrate and the diaphragm maybe capacitively coupled to form a fixed plate and a movable plate of avariable capacitor. Each carrier may be coupled to an insulator that iscoupled to the substrate. The diaphragm may be perforated and/orcorrugated. The space between the diaphragm and the at least one carriermay be in a nominal plane of the diaphragm. The diaphragm may be stressisolated from the at least one carrier. The at least one carrier mayinclude a single unitary carrier surrounding the diaphragm or mayinclude a plurality of distinct carriers. The at least one insulator mayinclude an oxide. The diaphragm assembly may include polysilicon. The atleast one insulator may be formed directly or indirectly on thesubstrate, and the at least one carrier may be formed directly orindirectly on the at least one insulator. The substrate may be formedfrom a silicon layer of a silicon-on-insulator wafer. The substrate mayinclude a number of throughholes, in which case the throughholes mayallow sound waves to reach the diaphragm from a back-side of thesubstrate. The microphone may include electronic circuitry that producesa signal in response to diaphragm movement. The electronic circuitry maybe formed direct or indirectly on the substrate.

In accordance with another aspect of the invention there is provided amicrophone including a substrate; a diaphragm; support means for movablycoupling the diaphragm to the substrate, the support means includingcarrier means for fixed coupling with the substrate and suspension meansfor movably coupling the diaphragm to the carrier means and spacing thediaphragm from the carrier means; and insulator means for electricallyisolating the diaphragm and the substrate.

In various alternative embodiments, the microphone may further includemeans for capacitively coupling the substrate and the diaphragm to forma fixed plate and a movable plate of a variable capacitor. Themicrophone may additionally or alternatively include means for allowingsound waves to reach the diaphragm from a back-side of the substrate.The microphone may additionally or alternatively include means forproducing a signal in response to diaphragm movement.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing advantages of the invention will be appreciated more fullyfrom the following further description thereof with reference to theaccompanying drawings wherein:

FIG. 1 shows the general structure of a micromachined microphone asknown in the art;

FIG. 2A schematically shows the bowing motion of a drum-like MEMSmicrophone diaphragm;

FIG. 2B schematically shows the plunging motion of a spring-attachedMEMS microphone diaphragm;

FIG. 3 schematically shows a MEMS microphone that may be produced inaccordance with illustrative embodiments of the invention;

FIG. 4 schematically shows a plan view of the microphone of FIG. 3configured in accordance with illustrative embodiments of the invention;

FIG. 5 shows a plan view photograph of a specific microphone configuredin accordance with illustrative embodiments;

FIG. 6 shows a close-up plan view picture of the spring shown in FIG. 5;

FIG. 7 schematically shows a cross-sectional and partial top view of amicrophone configured in accordance with illustrative embodiments of theinvention, with the diaphragm in an unreleased state; and

FIG. 8 schematically shows a cross-sectional and partial top view of amicrophone configured in accordance with illustrative embodiments of theinvention, with the diaphragm in a released state.

In order to facilitate interpretation of black-and-white reproductionsof certain figures, various materials are identified using the followinglegend: “S” indicates single-crystal silicon; “O” indicates oxide; “P”indicates polysilicon; “M” indicates metal; and “Pass” indicates apassivation material such as nitride.

Unless the context otherwise suggests, like elements are indicated bylike numerals. Also, unless noted otherwise, the drawings are notnecessarily drawn to scale.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In embodiments of the present invention, a MEMS microphone includes adiaphragm assembly supported by a substrate. The diaphragm assemblyincludes at least one carrier, a diaphragm, and at least one springcoupling the diaphragm to the at least one carrier such that thediaphragm is spaced from the at least one carrier. An insulator (orseparate insulators) between the substrate and the at least one carrierelectrically isolates the diaphragm and the substrate. The carrier maybe coupled directly to the insulator and the insulator may be coupleddirectly to the substrate; alternatively, one or more additionalmaterials may separate the insulator from the substrate and/or thecarrier. With the diaphragm and the substrate electrically isolated fromone another, the diaphragm and the substrate may be capacitively coupledand therefore may be used as the two plates of a variable capacitor inorder to convert audible signals to electrical signals.

FIG. 3 schematically shows an unpackaged MEMS microphone 10 (alsoreferred to as a “microphone chip 10”) in accordance with illustrativeembodiments of the invention. Among other things, the microphone 10includes a static backplate 12 that supports and forms a variablecapacitor with a diaphragm assembly including diaphragm 14 (details ofthe connection of the diaphragm assembly and the backplate 12 arediscussed below). In illustrative embodiments, the backplate 12 isformed from single crystal silicon, the diaphragm assembly includingdiaphragm 14 is formed from deposited polysilicon, and the insulatorbetween the backplate 12 and the diaphragm assembly is formed from anoxide. In this example, the backplate 12 is formed from the top siliconlayer of a silicon-on-insulator (SOI) wafer 20 and so rests on anunderlying oxide layer and a base silicon layer. To facilitateoperation, the backplate 12 has a plurality of throughholes 16 that leadto a back-side cavity 18 formed through the underlying oxide layer andthe base silicon layer. The microphone 10 may be used or packaged insuch a way that sound waves reach the diaphragm 14 through the back-sidecavity 18 and throughholes 16.

Audio signals cause the diaphragm 14 to vibrate, thus producing achanging capacitance. On-chip or off-chip circuitry converts thischanging capacitance into electrical signals that can be furtherprocessed. It should be noted that discussion of the microphone 10 shownin FIG. 3 is for illustrative purposes only. Other MEMS microphoneshaving similar or dissimilar structure to the microphone 10 shown inFIG. 3 therefore may be used with illustrative embodiments of theinvention.

FIG. 4 schematically shows a plan view of a microphone 10 configured inaccordance with illustrative embodiments. This exemplary microphone 10has many of the same features as those shown in FIG. 3. Specifically, asshown, the microphone 10 includes a substrate 20 with a plurality ofcarriers 22 (in this case, four carriers) that support the diaphragm 14via a plurality of springs 24. Unlike the diaphragm 14, each carrier 22is fixedly coupled with the substrate 20. In illustrative embodiments, alayer of electrical insulator material (e.g., an oxide) couples eachcarrier 22 to the substrate 20 and electrically insulates each carrier22 from the substrate 20.

Among other things, this arrangement forms an expansion space 26 betweenat least one of the carriers 22 and the diaphragm 14. Therefore, ifsubjected to stresses, the diaphragm 14 can freely expand into thisspace 26. Accordingly, under anticipated stresses, the diaphragm 14should not mechanically contact the carriers 22 (such contact coulddegrade system performance).

FIG. 5 shows a plan view photograph of a specific microphone 10configured in accordance with illustrative embodiments, while FIG. 6shows a close-up plan view picture of one spring 24 shown in FIG. 5. Itshould be noted that the specific microphones 10 are examples of variousembodiments of the invention. Accordingly, discussion of specificcomponents, such as the shape and number of springs 24, should not beconstrued to limit various embodiments of the invention.

As shown, the microphone 10 has a circular diaphragm 14 and fourradially extending but circumferentially shaped springs 24 that form thespace 26 between the carrier(s) 22 and the outer peripheral edge of thediaphragm 14. In this example, the diaphragm assembly includes a singleunitary carrier 22 surrounding the diaphragm 14. In addition toproviding the noted expansion space 26, the springs 24 also shouldmitigate diaphragm bowing (i.e., when the diaphragm 14 is concave whenviewed from its top) when moved downwardly. Accordingly, because ofthis, the diaphragm 14 should move toward the substrate 20 in a moreuniform manner than prior art designs having no space 26 or springs 24.For example, the diaphragm 14 may move upwardly and downwardly in amanner that approximates a plunger. Accordingly, the diaphragm 14 shouldbe able to move up and down more freely, and more area of the inner faceof the diaphragm 14 should be usable to produce the underlying signal.

FIG. 7 schematically shows a cross-sectional and partial top view of amicrophone 10 configured in accordance with illustrative embodiments ofthe invention, with the diaphragm in an unreleased state. This drawingschematically shows a number of features discussed above, such as thespace between the diaphragm 14 and the substrate 20, as well as thespace 26 between the diaphragm 14 and the carrier 22. In this figure,the diaphragm is shown with an underlayer of oxide, which is laterremoved in order to release the diaphragm. FIG. 8 schematically shows across-sectional and partial top view of a microphone configured inaccordance with illustrative embodiments of the invention, with thediaphragm in a released state (i.e., with the underlayer of oxideremoved).

In certain embodiments of the present invention, a micromachinedmicrophone may be formed from a silicon or silicon-on-insulator (SOI)wafer. As known in the art, a SOI wafer includes a top silicon layer,usually called the device layer, an intermediate insulator (oxide)layer, and a bottom silicon layer that is typically much thicker thanthe top silicon layer (e.g., approximately 650 microns). The top layerformed in either a silicon or a SOI wafer may be relatively thin (e.g.,approximately 10 microns thick) in some embodiments of the invention ormay be relatively thick (e.g., approximately 50 microns thick) in otherembodiments. In certain embodiments of the present invention, the fixedsensing electrode (also referred to herein as a “backplate”) may beformed from the top silicon layer of the wafer, and the diaphragm may beformed so as to be suspended above the top silicon layer. Perforationsmay be formed in the fixed sensing electrode to allow sound waves toreach the diaphragm from the bottom side of the wafer. An insulatinglayer (e.g., an oxide layer) on the back side of the top silicon layer,which may be the inherent oxide layer of a SOI wafer or an oxide layerdeposited on a silicon wafer, may be used as an etch stop layer forcontrolling the machining of the fixed sensing electrode.

An exemplary process for forming a micromachined microphone from an SOIwafer involves etching trenches through the top silicon layer of a blankSOI wafer into the intermediate oxide layer and optionally through tothe bottom silicon layer. The trenches are then lined with an oxidematerial. A polysilicon material is then deposited so as to fill thelined trenches and cover the top silicon. The polysilicon material ispatterned and etched to form various sacrificial structures that will beremoved later. Additional oxide material is deposited. A polysiliconmaterial is deposited and patterned to form the diaphragm assemblyincluding the microphone diaphragm and suspension spring. Oxide isdeposited, and holes are etched to expose portions of the backplate andthe diaphragm assembly. Metal is deposited and patterned in order toform an electrode for placing electrical charge on the diaphragm, anelectrode for placing electrical charge on the backplate, and aplurality of bond pads. There may be electrical connections between bondpads and the electrodes. Passivation layers (e.g., an oxide layercovered by a nitride layer, which is a standard passivation layer usedfor integrated circuitry) are then deposited. The passivation layers areetched to expose the bond pad and to expose the diaphragm. Photoresistmaterial is deposited and then patterned to expose a future pedestalarea. The oxide at the future pedestal area is then removed by etching.The remaining photoresist material is removed, and the bottom siliconlayer is optionally thinned from approximately 650 microns toapproximately 350 microns by any of several methods including etching,grinding and polishing. Photoresist material is deposited on the frontside of the wafer so as to form a photoresist pedestal. Photoresistmaterial is also deposited on the back side of the wafer and patternedto outline a backside cavity. The backside cavity is formed by etchingaway a portion of the bottom silicon layer to the intermediate oxidelayer. In an exemplary embodiment, the backside cavity after packagingis approximately one cubic millimeter in volume. A portion of theintermediate oxide layer within the cavity is removed in order to exposethe sacrificial polysilicon structures. The sacrificial polysiliconstructures are removed, e.g., by exposing the polysilicon to XeF₂ gas oranother suitable silicon etchant through the backside cavity. It shouldbe noted that the XeF₂ gas may remove some of the exposed bottom siliconlayer, although this is generally undesirable. The oxide behind thediaphragm is removed, e.g., by placing in an appropriate liquid. Then,the front side photoresist material (including the pedestal) is removed,e.g., in a dry etch (not a liquid). This essentially releases thediaphragm and related structures. It should be noted that the pedestalis used to support the delicate microphone structures during release andmay not be required in all embodiments, particularly if vapor HF is usedto remove the oxide instead of a liquid.

An exemplary process for forming a micromachined microphone from aregular silicon wafer involves depositing an oxide layer on the siliconwafer. Then, a polysilicon material is patterned and etched to form thediaphragm assembly. An oxide material is deposited, and holes are etchedto expose portions of the substrate and the diaphragm assembly. Metal isdeposited and patterned in order to form bond pads and electrodes forplacing charge on the microphone diaphragm and backplate. There may beelectrical connections between the bond pads and one or more of theelectrodes. Passivation layers (e.g., an oxide layer covered by anitride layer, which is a standard passivation layer used for integratedcircuitry) are deposited. The passivation layers are etched to exposethe bond pads. A portion of the passivation layers above the microphonestructures is removed and the oxide over and partially under thepolysilicon structures is removed to form resist pedestal areas. Theback side of the silicon wafer is optionally thinned from approximately650 microns to approximately 350 microns by any of several methodsincluding etching, grinding and polishing the back side, and a layer ofoxide is deposited on the back side of the wafer. A photoresist materialis deposited on the front side of the wafer, and the oxide on the backside of the wafer is patterned. A photoresist material is deposited andpatterned on the back side of the wafer, and trenches are etched intothe silicon wafer. The photoresist material is removed from both thefront side and the back side, and a new layer of photoresist material isdeposited on the front side for protection. Cavities are then etched inthe back side of the wafer using the existing oxide as a hard mask. Thetrenches are then further etched through the silicon layer to the resistpedestal areas of the microphone region. The oxide exposed through thecavities is removed, e.g., by exposing to HF gas. The remainingphotoresist material is removed from the front side of the wafer,thereby releasing the microphone structures. Finally, borosilicate glassmay be aligned and anodic bonded to the back side of the wafer.Microphone holes may be ultrasonically cut in the glass prior tobonding.

It should also be noted that these described processes are exemplaryonly. For any particular implementation, fewer, additional, or differentsteps or processes may be utilized. In some cases, materials differentthan those described may be suitable for a particular step or process.It would be virtually impossible to describe every combination andpermutation of materials and processes that could be employed in variousembodiments of the invention. Therefore, the present invention isintended to include all such materials and processes including suitablevariations of the materials and processes described. Furthermore,micromachined microphones of the types described above may be formed onthe same wafer along with an inertial sensor and/or electronic circuitryand may be packaged in a variety of form factors.

It should also be noted that the present invention is not limited to anyparticular shape, configuration, or composition of microphone diaphragm.The microphone may be, for example, round or square, solid or perforatedby one or more holes, and/or flat or corrugated. Different diaphragmconfigurations might require different or additional processes fromthose described. For example, additional processes may be used to formholes or corrugations in the diaphragm. In various embodiments describedabove, the diaphragm assembly is polysilicon, but other materials may beused.

It should also be noted that the present invention is not limited to anyparticular type or number of springs for coupling the diaphragm to theat least one carrier. Embodiments of the present invention may usedifferent types and numbers of springs. For example, various embodimentsof the present invention may use spring types and configurationsdescribed in the related application having Ser. No. 60/885,314 andhaving attorney docket number 2550/B40, which was incorporated byreference above.

It should also be noted that the present invention is not limited to anyparticular type of insulator between the substrate and the at least onecarrier. In various embodiments described above, the insulator is anoxide, but other types of insulators may be used.

It should also be noted that the present invention is not limited to anyparticular type of packaging. For example, various embodiments of thepresent invention may use packaging techniques described in the relatedapplications having Ser. Nos. 11/338,439, and 11/366,941, and havingattorney docket numbers 2550/A87 and 2550/A88 respectively, both ofwhich were incorporated by reference above.

Although the above discussion discloses various exemplary embodiments ofthe invention, it should be apparent that those skilled in the art canmake various modifications that will achieve some of the advantages ofthe invention without departing from the true scope of the invention.

1. A microphone comprising: a substrate comprising a backplate, whereinthe backplate further comprises a plurality of throughholes, and whereinthe backplate forms a fixed plate of a variable capacitor; a diaphragmassembly supported by the substrate, the diaphragm assembly including atleast one carrier, a conductive diaphragm, and at least one springcoupling the diaphragm to the at least one carrier, the diaphragm beingspaced from the at least one carrier; and at least one insulator betweenthe substrate and the at least one carrier so as to electrically isolatethe diaphragm and the substrate, wherein the diaphragm forms a movableplate of the variable capacitor.
 2. A microphone according to claim 1,wherein each carrier is coupled to an insulator and wherein suchinsulator is coupled to the substrate.
 3. A microphone according toclaim 1, wherein the diaphragm is perforated.
 4. A microphone accordingto claim 1, wherein the diaphragm is corrugated.
 5. A microphoneaccording to claim 1, wherein the diaphragm has a plane when unflexed,the at least one spring producing a space between the diaphragm and theat least one carrier in the direction of the plane of the diaphragm. 6.A microphone according to claim 1, wherein the diaphragm is stressisolated from the at least one carrier.
 7. A microphone according toclaim 1, wherein the at least one carrier comprises a single unitarycarrier surrounding the diaphragm.
 8. A microphone according to claim 1,wherein the at least one carrier comprises a plurality of distinctcarriers.
 9. A microphone according to claim 1, wherein the at least oneinsulator comprises an oxide.
 10. A microphone according to claim 1,wherein the diaphragm assembly comprises polysilicon.
 11. A microphoneaccording to claim 1, wherein the at least one insulator is formeddirectly or indirectly on the substrate.
 12. A microphone according toclaim 11, wherein the at least one carrier is formed directly orindirectly on the at least one insulator.
 13. A microphone according toclaim 1, wherein the substrate is formed from a silicon layer of asilicon-on-insulator wafer.
 14. A microphone according to claim 1,wherein the throughholes allow sound waves to reach the diaphragm from aback-side of the substrate.
 15. A microphone according to claim 1,further comprising electronic circuitry that produces a signal inresponse to diaphragm movement.
 16. A microphone according to claim 15,wherein the electronic circuitry is formed direct or indirectly on thesubstrate.
 17. A microphone comprising: a substrate comprising abackplate, wherein the backplate further comprises a plurality ofthroughholes; a conductive diaphragm; support means for movably couplingthe diaphragm to the substrate, the support means including carriermeans for fixed coupling with the substrate and suspension means formovably coupling the diaphragm to the carrier means and spacing thediaphragm from the carrier means; insulator means for electricallyisolating the diaphragm and the substrate; and means for capacitivelycoupling the backplate and the diaphragm to form a fixed plate and amovable plate, respectively, of a variable capacitor.
 18. A microphoneaccording to claim 17, further comprising means for allowing sound wavesto reach the diaphragm from a back-side of the substrate.
 19. Amicrophone according to claim 17, further comprising means for producinga signal in response to diaphragm movement.
 20. A method of operating amicrophone, the method comprising: providing a substrate comprising aconductive backplate, wherein the backplate forms a fixed plate of avariable capacitor; providing a diaphragm assembly supported by thesubstrate, the diaphragm assembly including at least one carrier, aconductive diaphragm, and at least one spring coupling the diaphragm tothe at least one carrier, the diaphragm being spaced from the at leastone carrier; providing at least one insulator between the substrate andthe at least one carrier so as to electrically isolate the diaphragm andthe substrate, wherein the diaphragm forms a movable plate of thevariable capacitor; and exposing the microphone to sound waves wherebythe at least one spring flexes to change the capacitance formed by thediaphragm and the backplate.